For some time now, researchers have been attempting to develop an optical fiber or lightpipe for CO.sub.2 laser wavelengths (i.e., 10.6 micrometers). The lightpipe should be flexible, have a transmittivity greater than 90 percent per meter, and be capable of transmitting power levels in excess of fifty watts. This flexible lightpipe, which can exceed one meter in length and have an inner diameter of about one millimeter, should also be easily manufactured, inexpensive, and non-toxic. Lightpipes having such properties are suitable for numerous military, scientific, medical, and industrial applications.
A variety of approaches to this development problem have been taken, some meeting with limited success. There are several existing solid-type lightpipes relying on total internal reflection, but none of these has yet reached commercial realization. The hollow waveguide described by Katherine D. Laakmann in U.S. Pat. No. 4,652,083 is available commercially, but suffers from limited flexibility and length. It is also difficult to manufacture because of the difficulty in depositing one or more thin film layers of precise thickness onto the interior wall of a long, narrow lightpipe.
It is therefore desirable to have a material whose refractive index is such that it will produce high light reflectivity from the internal surfaces of a hollow lightpipe of all polarizations of light over grazing angles of light incidence.